The present invention relates to an X-ray lithographic apparatus.
In general, exposure in vacuum and exposure in the atmosphere are considered as the exposure systems of X-ray lithographic apparatuses.
In the vacuum exposure system having heretofore been principally practised, a wafer is exposed to radiation with both a mask and the wafer placed in a vacuum chamber in which an X-ray source is disposed. Since the X-ray flux does not come out of the vacuum chamber, it attenuates little, and the exposure efficiency is high. Since, however, the mask and the wafer must be handled and positioned in the vacuum chamber, the problems of low available percentage etc. have been involved.
Therefore, the atmospheric exposure in which a wafer is placed in the atmosphere and is exposed to radiation has formed the mainstream.
In the atmospheric exposure system, an X-ray source is placed in a vacuum chamber, and the wafer which is as proximate to a mask as ten .mu.m--several tens .mu.m is irradiated with the generated X-rays through a gastight chamber which is filled with helium gas or the like, easy to transmit the X-rays, under a pressure of approximately 1 atmosphere, as well as the mask which is mounted on one end of the gastight chamber. Accordingly, the mask must be so mounted that one surface confronts the gastight chamber filled with the helium gas or the like, while the other surface confronts the atmosphere. Moreover, since the X-rays attenuate greatly due to the helium gas or the like in the atmospheric exposure system, the mask is required to be as thin as possible. This has led to the occurrence of the problem that the mask vibrates on account of the pressure difference between the atmosphere and the gastight chamber filled with the helium gas or the like.
In this regard, a method is considered wherein the pressure difference between the atmosphere and the gastight chamber is detected and wherein the pressure of the helium gas or the like in the gastight space is controlled by a pressure regulator valve. With this method, however, a detection lag and the operation lag of the pressure regulator valve are involved. Another problem is the pressure regulation precision of the pressure regulator valve.